Diamond-containing abrasive substance



Oct. 17, 1944.

R. A. 1.. SELIGMAN ET AL ,360,798 DIAMOND-CONTAINING ABRASIVE' SUBSTANCE Filed Dec. 12, 19 42 2 Sheets-Shei; 1

ATTORNEYS Oct. 17, 1944.

R. A. L. SELIGMA N ET AL 2,360,793 DIAMOND-CONTAINING ABRASIVE SUBSTANCE Filed Dec. 12, 1942 2 Sheets-Sheet 2 ATTORNEYS,

Patented Oct. 17, 1944 DIAMOND-CONTAINING ABRAsmi:

- SUBSTANCE Roger A. L. Seligman and Hans Heinrich Schwarzkopf, New York, and John G. Van tterloo, Yonkers, N. Y., assignors, by mesne assignments, to said Seligman Application December 12, 1942, Serial No. 468,748

9 Claims.

This invention relates to a method of securing masses of fine-mesh diamond particles in a metallic matrix securely aflixed to the supporting metal shank of any kind of grinding or cutting tool, and to the article so made.

Two kinds of diamond-charged abrasive wheels or grinding tools are now commercially available, wherein the diamond particles are disposed in depth within a supportin matrix. In one of these, illustrated by the Sanford Patent No. 1,981,970, the matrix consists of heat-settable' resmoid such as the type commonly known in the art under the trade-name Bakelite. In the other the matrix consists of powdered metal, the metal particles being often as small as the diamond particles, mixed with the diamond particles in powdered form and then subjected to heavy pressure and sintering temperatures to form a solid cohesive body with diamond particles embedded therein. Of these two types of wheels or tools, the latter (having a metallic matrix) has fields of usefulness not reached by those having the resinoid matrix.

Efforts have been made heretofore to form the matrix of electrodeposited metal. This is relatively easy in the mounting of relatively large diamond fragments which can be individually handled, but these methods have not been successful in dealing with fine-mesh diamond particles. For example, if the diamond particles are ISO-mesh size, there will be approximately 22,000

particles ineach square inch when distributed in one layer" and methods of individual handling and mounting are commercially impracticable. Nor will ordinary plating methods, such as that shown in the Case Patent No. Re. 12,567, give a satisfactory diamond-containing matrix, for a considerable number of diamonds for some reason will always be loosely secured in the metal and tear out easily when the tool is put to work. Such methods also result in voids forming in the matrix, with resulting weakness thereof.

The present invention has for its object the production of'a diamond-charged tool or wheel wherein fine diamond particles are all securely held in an electro-deposited metallic matrix which possesses certain marked advantages'over -matrices made by the compression and sintering of powdered metal. The advantages of the new type wheel made according to our invention "appear to be: (a) that a greatly increased concentration of diamond particles can be obtained within an adequate metallic matrix and with the diamonds disposed in depth; (b) that the change in size of the wheel, resulting from its doing a given amount of work, is much less than wheels wherein the matrix consists of sintered metal powder; (c) that the diamond-containing matrix appears to be stronger and more resistant to chipping at the edges than other forms of matrices, and (d) the diamond-containing matrix as a whole, notwithstanding the fact it is electrodeposited, is bonded to the underlying metallic shank with substantially the same strength as matrices made of powdered metal.

Referring to the annexed drawings:

Fig. 1 shows, in cross section, a grinding wheel in a plating bath where its surface to be plated is receiving a deposit of diamond-containing metallic matrix, the parts being at rest and the electric current flowing.

Fig. 2 shows the apparatus of Fig. 1 at the moment when the mass of diamond particles adjacent'the surface being plated has been caused to shift abruptly relative to that surface.

Figs. 3 to 8, inclusive, show in cross-section on a larger scale the successive stages ofgrowth in the electroplating bath of a diamond-containing metallic matrix according to our invention, the successive views epresenting thefollowing stages Fig. 3 shows the fresh surface to be plated after the mass of diamond particles have settled thereon at the beginning of the plating opration.

Fig. 4 shows the surface during the first stage of movement and disturbance, the mass of diamond particles being temporarily suspended in the agitated liquid above.

Fig. 5 shows the surface after the mass of diamond particles has once more settled thereon for a period of quiescence.

Fig. 6 shows a subsequent stage of disturbance, during which the diamond mass is in suspension in the liquid and a layer of diamond-containing metallic matrix of some depth has formed upon the surface of the tool.

Fig. 7 corresponds to Fig. 5, but at a later stage.

Fig. 8 corresponds to Fig. 6, but at a later stage.

Fig. 9 is a fragmentary section of a plating bath showing the heads of two small tools, for example, dental tools, projecting through a rubber pad into the plating fluid and being there buried in a mass of diamond particles which surrounds their exposed tips on all sides.

Fig. 10 showsthe arrangement of Fig." 9 during the period of disturbance when the mass of diamond particles is shifting abruptly relative to the surfaces on which plating has been accomplished.

Fig. 11 shows in elevation, and Fig. 12 in part section, the results of the types of plating operation indicated in Fig. 9.

Fig. 13 shows in greatly enlarged section the structure which is produced in accordance with one form of our invention.

Referring to the operation shown in Figs. 1 and 2: Within a suitable tank 20 is placed a body of plating solution 2| and a metallic anode 22. Assuming that the matrix is to be nickel, the anode is of that metal and the solution is one of the usual nickel-plating solutions. A grinding wheel blank 23, usually of brass, is mounted on the end of a post 24 provided with a handle 25 and appropriately sheathed as with rubber 26. The surface 21 is the surface on which the abrasive layer is to be formed, and, in the arrangement shown, this is disposed to lie in a horizontal plane when in submerged position. We usually mask the surfaces which are not to be plated by a disc 28 and an annulus 29 of some suitable non- :metallic material which can be easily machined, -such for example as the transparent glass-like plastic which is sold under the trade-name Plexiglas. Preferably, in the type of operation shown in Figs. 1 and 2, the upper surfaces of the disc 28, the annulus 29, and the surface 21 to be plated, are arranged to lie in the same plane. Temporary sheathed or insulated supports 30 are arranged to keep the central portion of the wheel elevated above the mass of diamond particles mentioned below. Incidental nickel plating (but without inclusion of diamond particles) on the undersurface of blank 23 is permitted.

In the bath 2| we place a large excess of diamond particles. For practical purposes, we deal in the operation here disclosed with diamond particles smaller in size than GO-mesh. Our invention works well in handling particles as small as 400-mesh. The ratio of diamond particles present in the bath to diamond particles which it is desired to include in the matrix may be varied within wide limits, provided always there is a substantial excess of the former over the latter. In a typical operation of the character shown in Figs. 1 and 2, the bath consists of about four gallons of liquid and contains approximately 400 carats of 150- mesh diamond powder; and the annular surface 21 has an area of approximately 18 sq. in. and is to be plated to a depth sufiicient to form thereon a matrix containing approximately 18 carats of diamonds. Thus, in the typical case suggested above, more than twenty times as many diamond particles are contained in the bath as are intended to be secured in the diamond-containing matrix deposited on surface 21. This ratio is not fixed or critical, but according to our understanding of the invention a large excess of diamond particles should be present in the plating bath.

The post 24 is connected by wire 3|, and the anode 22 is connected by wire 32, to a suitable source of electric current whose voltage depends upon thecharacteristics of the bath, the metal being used for plating, and other well-known factors. In the operation mentioned above, we use an applied voltage of 1.8 volts.

When the bath has been prepared, and before the wheel 23 has been inserted therein, the mass of diamond particles appears as a layer at the bottom of the bath. indicated by the reference character 33. At the commencement of operation, and at the moment when the wheel 23 is inserted into the bath, the liquid is agitated sufficiently to cause the diamond particles to become suspended therein and make the bath cloudy.

This may be done by moving the handle 25 up and down to agitate the liquid and carry the diamond particles into suspension. When the wheel comes to rest as shown in Fig. 1, the suspended diamond particles fall as the liquid becomes quiescent, forming a layer 34 of substantial thickness over the top of the wheel and its masking elements, and resting on the surface 21 to be plated.

As shown in Fig. 3, this mass 34 rests upon the surface 21 of wheel 23 and in contact therewith. After a suitable interval of time, set forth below, the handle 25 is grasped by the operator and the wheel is moved sufficiently to shift abruptly the mass of diamond particles which have been in contact with surface 21. This may be done by moving the wheel up and down while still submerged, but we prefer to raise the wheel as indicated in Fig. 2 so that it becomes tipped and the diamond particles in contact with surface 21 slide by gravity into the bath, and by rotation of the wheel surface 21 is brought above the surface of the bath and is washed thereby. After this movement, in which the mass of loose diamond parti cles adjacent to surface 2'! slides along and in contact with that surface, the wheel is then returned to its original position, the diamond particles fall once again upon it, and the wheel is left undisturbed in this position for a further period of plating.

At intervals thereafter the described operation is repeated, periods of quiescence and plating alternating with periods in which the mass is abruptly shifted relative to the surface on which plating is taking place, until a diamond-containing matrix of electrodeposited material has been built up to the desired depth.

The length of the periods of quiescent plating between abrupt movements will depend somewhat on the character of the surface on which the diamond-containing matrix is being deposited. In general, the initial period of quiescent plating at the commencement of the plating operation should be long enough to secure the first layer of diamond particles to an extent such that, upon the first disturbance, some at least will remain secured in position. Thereafter the length of the periods of quiescent plating will depend on the nature of the tool on which the abrasive layer is being deposited, and other factors. For example, on certain types of tools, at the voltages used, the initial period of quiescent plating is four hours, then the first abrupt movement of the diamond mass mentioned above is effected; thereafter in the case of tools without sharp points the periods of quiescent plating may last from two to three hours each, but in the case of tools with sharp points these periods may be approximately an hour in length.

The effect of the abrupt movement of the mass of diamonds in contact with the surface being plated is to cause a greatly increased concentration (in the ultimate diamond-containing metal matrix) of diamond particles over the concentration possible when using compressed and sintered metal powder to hold them, and to sliminate'from the matrix diamond particles which have become in some way defectively secured and would, if left undisturbed, constitute weak spots in the matrix. Quiescent plating without abrupt movement from time to time has been found in produce a matrix in which an appreciable percentage of the diamonds are loosely or defect-l vely secured in place, with the result that when the wheel is put to use these diamonds readily tear loose and being numerous constitute an important loss factor. v

We do not know the reason for this phenomenon. We have, however, found that plating in the presence of a large excess mass of diamond particles will produce a metallic matrix in which all diamond particles enclosed in the matrix are tightly and securely held, if the diamond mass adjacent the surface being plated is abruptly moved or disturbed from time to time during the plating operation as herein described. Our supposition is that movement of the unattached diamond mass across the surface being plated tends to test out the secureness of attachment of the individual diamond particles which have become partly embedded in the metal and leaves behind those which have become securely attached and loosens and removes those which are in process of being secured in a defective manner such that they will afterwards be likely to tear out when the wheel is used for grinding or cutting purposes.

Having overcome what seems to be the chief obstacle in the way of using, an electrodeposited matrix to secure diamonds of size smaller than 60-mesh (which cannot practicably be handled as individuals) we have discovered that in the resulting diamond-and-matrix mass we can incorporate a very much larger percentage by volume of diamonds than can be incorporated in a mass whose matrix consists of pressed and sintered metallic powder, thereby producing notable advantages in use. By means of our invention we have made diamond-containing electroplated nickel masses, the diamond particles being smaller in size than 60-mesh and deposited in depth in such manner as to be the equivalentof "several layers, in which the diamonds comprise upwards of 30 per cent by volume of the entire diamond-and-nickel mass. This figure can be shown by dissolving in acid a mass of known dimensions and weighing the released diamonds.

This concentration appears to be materially higher than the concentration to be found in the best wheels now commercially available whose matrix consists of pressed and sintered metal powder. A direct comparison by the acid-dissolution test is not feasible because of the error introduced by the presence of voids in the metal powder matrices, but a reliable comparison can be made by comparing diameter losses in use.

Diamond-charged grinding wheels, wherein the diamonds are smaller than 60-mesh and are held in a matrix of pressed and sintered metal powder, are commercially available in various degrees of diamond concentration, the highest concentration being known as 100. Such wheels are often or customarily made in which the diamond-containing mass is in the form of a continuous layer of material around its periphcry a: or .031 inch thick. Such layer, when it reaches the end of its useful life and the wheel can no longer be' used, has usually been reduced to a thickness of about .003 to .004 inch. The difference represents eter of about .054 inch.

For purposes of comparison we made up a diamond-charged grinding wheel according to the procedure and method described above. corporated in its nickel matrix diamond particles of the same mesh size as those forming part of the wheel previously mentioned. We permitted plating to proceed till the diamond-and-nickel mass had a thickness of about .010 inch to the We ina reduction in wheel diamplane representing the average level of the top of the nickel, and about .012 inch to the plane representing the average level of the tops of the protruding diamonds. The eifective life of this wheel was found to be about the same as that of the wheel previously mentioned above, indicating that the number of diamond particles underlying each square inch of superficial surface of the abrasive mass when new was about the same in both wheels. When the wheel made in accordance with our invention would no longer cut, there remained approximately .003 or .004 in. of the nickel mass on its surface. Thus, in performingthe same work as the wheel previously mentioned, the wheel made in accordance with our invention had suffered a reduction in diam eter of about .016 in. or less than a third that of the wheel previously mentioned.

These tests indicate that the concentration of diamond particles in an abrasive mass made in accordance with our invention is more than three timesthat of the highest commercially-available Accordingly, we believe that the use of our invention makes possible the manufacture of a new article of annexed claims, which is the characteristic and novel product of our process.

In applying a diamond-containing electrodeposited matrix on the surface of a small drill is vertically disposed while in the plating bath. To accomplish this result we arrange one or more of the drill points to be plated in such manner through small holes in the bottom of the bath. This is shown, for example, in Fig. 9 where two small dgillfifi. are shown secured in drillings in the bottom 36' of a glass receptacle, using a perforated rubber sheet 31 to previously described, except that the mass of sufiiciently deep so that also with the exposed cylindrical surfaces thereof adjacent the heads. At desired intervals the bath may be tipped or rocked or (if wholly enclosed) may be inverted and shaken, to produce the required abrupt movement or shifting of the mass of loosediamond particles with respect to the surfaces on which Such movement is indicated in Fig. 10. It may be repeated at intervals, as required, with intervening periods of quiescent plating in the position shown in Fig. 9 until the desired thickness of diamond-containing electroplated matrix 4! commerce, as set forth in the plating is taking place.

plating bath, it may be helpful if the liquid does not entirely fill the container. In that case, when the container is inverted, the heads 40 may for a moment be freed entirely from contact with the bath itself, which facilitates the carrying out of the operation disclosed. In these cases, as in the previous arrangements mentioned, the bath consists of a suitable electrolyte for the metal being plated, and the anode consists of that metal, with suitable connections to a constant potential source of direct current as previously described.

The metal which we use for plating is preferably nickel, because of its hardness when electrodeposited. Other metals which may be used for this purpose are chromium, cobalt, palladium, rhodium and alloys of the same.

In certain cases these metals do not adhere to the metal of the shank with the desired certainty. This is especially true where the metal of the shank is steel and the matrix metal is nickel. In such cases (refer to Fig. 13) we proceed as follows: the surface 42 of the steel shank 53, after first being cleaned and polished, is plated with a thin layer of gold 44. The surface 45 of the gold then becomes the surface on which the diamond-containing electrodeposited nickel matrix is to be laid in accordance with the process described above. After this matrix has been built up to the desired degree of thickness, as

above set forth, the tool is then removed from the bath, rinsed, dried, and introduced into a furnace where it is heated in an atmosphere of hydrogen or other non-oxidizing gas to a temperature sufficient to cause interpenetration or sintering of the gold to the steel, and the nickel to the gold. For this purpose we maintain the furnace at a temperature of about 150 below the melting point of gold, namely, at a temperature of about 850 C. The tool is kept at this temperature from twenty minutes to half an hour. Under these conditions the goldappears to form a strong and effective bond between the nickel and the steel, whereby to prevent pealing of the matrix from the steel shank.

This heating operation, however, softens the nickel to an appreciable extent, either by an action analogous to annealing or by driving out the small molecular quantities of hydrogen which may be deposited with it.

After heating, accordingly, we then return the tool to a nickel plating bath (without diamonds) and build up a further deposit of nickel around and among the protruding diamond particles,until the particles which occupy the highest position in the mass are almost but not quite completely covered. This final layer of electrodeposited nickel affords an exceedingly hard outer surface and constitutes a solid anchoring medium for the entire abrasive mass.

In the manufacture of all tools in accordance with our invention whether or not they have been subjected to the action of the hydrogen furnace, it is desirable to apply a finish layer of nickel, or other metal, in a bath from which diamond particles are absent.

provides a finish coat, is very hard, and can be built up until the diamonds in the highest level 7 within the mass have been shrouded to the extent desired.

We claim:

1. The method of forming upon a metal surface an abrasive layer consisting of dust-like diamond particles secured within a hard metallic matrix which includes the steps of electroplating This final layer matrix metal uponsaid metal surface in an electroplating bath containing a mass of diamond particles substantially in excess of the number of particles required for the desired abrasive layer, and intermittently causing the particles adjacent said surface to shift abruptly relative to said surface after a' period of electroplating during which part at least of said mass of particles has remained relatively motionless in contact with said surface.

2. The method of forming upon a metal surface an abrasive layer consisting of dust-like diamond particles secured within a hard metallic matrix which includes the steps of electroplating matrix metal upon said metal surface in an electroplating bath containing a mass of diamond particles substantially in excess of the number of particles required for the desired abrasive layer, at least part of said mass being in contact with said surface, intermittently causing the said surface and the particles adjacent thereto to move abruptly relative to each other, and then continuing the electroplating while the bath and its contents remain relatively motionless with at least part of said mass of particles in contact with the surface being plated.

3. The method of forming upon a metal surface an' abrasive layer consisting of dust-like diamond particles secured within a hard metallic matrix which includes the steps of electroplating matrix metal upon said metal surface in an electroplating bath containing a mass of loose diamond particles in Contact with said surface for a period of time long enough to cause some at least of said particles to become embedded in matrix metal electrodeposited on said surface, and then, alternately, abruptly shifting said mass relative to said surface, and permitting said mass to rest in contact with the electrodeposited surface between shifts for a period of time long enough for some at least additional particles to become embedded in matrix metal electrodeposited on said surface, until a metallic matrix of the desired thickness has been built up on said surface, said matrix containing diamond particles which are closely spaced, securely held and disposed in depth.

4. The method of forming upon a metal surface an abrasive layer consisting of dust-like diamond particles secured within a nickel matrix which includes the steps of electroplating nickel upon said metal surface in a nickel-plating bath containing a mass of diamond particles substantially in excess of the number of particles required for the desired abrasive layer, and intermittently causing the particles adjacent said surface to move abruptly relative thereto after a period of electroplating during which at least part of said mass of particles has remained relatively motionless in contact with said surface.

5. The method of forming upon a metal surface an abrasive layer consisting of dust-like diamond particles secured within a nickel matrlx which includes the steps of electroplating nickel upon said metal surface in a nickel-plating bath containing a mass of diamond particles substantially in excess of the number of particles required for the desired abrasive layer, at least part of said mass being in contact with said surface, intermittently causing the said surface and the particles adjacent thereto to move abruptly relative to each other, and then continuing the electroplating while the bath and its contents remain relatively motionless with at thickness has been of particles in contact plated.

6. The method of forming upon a metal surface an abrasive layer consisting of duct-like diamond particles secured within a nickel matrix which includes nickel upon said metal surface in a nickel-plating bath containing a mass of loose diamond particles in contact with said surface for a period of time long enough to cause some at least of said particles to become embedded in nickel, and then, alternately, abruptly shifting said mass relative to said surface, and permitting said mass to rest in contact with the nickel between shifts for a period of time long enough for some at least additional particles to become embedded in nickel, until a nickel matrix of the desired built up on the original metal surface, said nickel matrix containing diamond particles which are closely spaced, securely held and disposed in depth.

'7. The method of formingupon a metal surface an abrasive layer consisting of dust-like diamond particles secured within a nickel matrix which includes the steps of plating a thin layer of corrosion-resistant metal upon said surface, electroplating nickel on the surface of said corrosion-resistant metal in the presence of a mass of diamond particles substantially in excess of the number of particles required for the desired layer, causing the particles adjacent the surface being plated to .shift abruptly relative thereto, heating the plated article to a temperature high enough to cause the metal of the original surface and the corrosion-resistant metal, and the nickel and the corrosion-resistant metal, to inter-diffuse without melting, and electroplating nickel in the absence of diamond particles on the surface of the previously deposited nickel.

8. The method of forming upon a metal surthe steps of electroplating aces 19s face an abrasive layer consisting of dust-like diamond particles secured within a nickel matrix which includes the steps of plating a thin layer of gold upon said surface, electroplating nickel on the surface of said gold in the presence of a mass of diamond particles substantially in excess'of the number of particles required for the desired layer, causing the particles adjacent the surface being plated to shift abruptly relative thereto, heating the plated article to a temperature high enough to cause'the metal of the original surface and the gold, and the nickel and the gold, to inter-diffuse without melting, and electroplating nickel in the absence of diamond particles on the surface of the previously deposited nickel.

9. The method of forming upon a metal surface an abrasive layer consisting of dust-like diamond particles secured within a hard metal matrix which includes the steps of electroplating matrix metal upon said metal surface in an electroplating bath containing a mass of loose diamond particles of which at least a few are in contact with said surface for a period of time long enough to cause some of said particles to become embedded in the matrix metal deposited on said surface and then alternately, abruptly shifting said mass relative to said surface and permitting at least a few of the particles in said mass to rest in contact with the electro-deposited. metal for a period of time long enough for some additional particles to become embedded in said matrix metal until a metal matrix of the desired thickness has been built up on. the original metal surface, said metal matrix containing diamond particles which are closely spaced, securely held and disposed in depth.

ROGER A. L. SELIGMAN. HANS HEINRICH SCHWARZKOPF. JOHN G. VAN OTTERLOO. 

